NVIDIA GeForce GT 645M vs NVIDIA GeForce GT 640M

NVIDIA GeForce GT 645M

The NVIDIA GeForce GT 645M is a mid-range, DirectX 11.1 compatible graphics card that was announced in the third quarter of 2012 for laptops. It is a faster clocked GeForce GT 640M and therefore also based on the Kepler GK107 architecture manufactured in 28nm at TSMC. The graphics card uses a 128-Bit wide memory interface with either the more common but slower DDR3 for VRAM or the more expensive and faster GDDR5.

Architecture

The Kepler architecture is the successor to the Fermi architecture that first appeared in laptops with the GeForce 400M series. The GK107 Kepler core offers two shader blocks, called SMX, each with 192 shaders for a total of 384 shader cores that are clocked at the same speed as the processor core. Although more shader cores are available in the Kepler architecture as compared to the Fermi design, the Kepler shaders are still expected to be up to twice as power efficient. However, due to the missing hot clock of the shader domain, two shaders of a Kepler chip are as fast as one shader of a Fermi chip (the latter is clocked twice as fast). PCIe 3.0 is now supported by the mobile Kepler series and an optional Turbo mode can automatically overclock the Nvidia card by a theoretical 15 percent if the laptop cooling system allows it. The implementation of this boost mode is done in the BIOS, but it is ultimately dependent upon the manufacturer of the laptop.

Performance

The gaming performance of the GeForce GT 645M equipped with DDR3 graphics memory depends on the 3D clock in the used laptop and is slightly above an average GT 640M. Therefore demanding games like Battlefield 3 are playable in 1366x768 and medium settings. Older and less demanding games, such as Modern Warfare 3, are easily playable with maxed out settings and high resolutions.

Features

The improved feature set now includes support for up to 4 active displays. Furthermore, high resolution monitors of up to 3840x2160 pixels can now be connected using DisplayPort 1.2 or HDMI 1.4a if available. HD-Audio codecs, such as Dolby TrueHD and DTS-HD, can be transmitted via bitstream mode through the HDMI port. However, as most laptops will feature Optimus, the integrated GPU will likely have direct control over the display ports and may limit the feature set available by the Nvidia Kepler cards.

The 5th generation PureVideo HD video processor (VP5) is also integrated in the GK107 core and offers hardware decoding of HD videos. Common codecs such as MPEG-1/2, MPEG-4 ASP, H.264 and VC1/WMV9 are fully supported up to 4K resolutions while VC1 and MPEG-4 are supported up to 1080p. Two streams can be decoded in parallel for features such as Picture-in-Picture. Another novelty is the inclusion of a dedicated video encoding engine similar to Intel QuickSync that can be accessed by the NVENCI API.

The power consumption of the GeForce GT 645M should be similar to the GT 640M and therefore a bit below that of the older GeForce GT 540M and more in line with the GT 525M. As a result, the Nvidia GPU is best suited for multimedia notebooks 14-inches or greater.

NVIDIA GeForce GT 640M

The NVIDIA GeForce GT 640M is a mid-range, DirectX 11.1 compatible graphics card that was announced in the first quarter of 2012 for laptops. It is a Kepler-based GPU built on the GK107 architecture and is manufactured in 28nm at TSMC. The graphics card uses a 128-Bit wide memory interface with either the more common but slower DDR3 for VRAM or the more expensive and faster GDDR5.

Architecture

The Kepler architecture is the successor to the Fermi architecture that first appeared in laptops with the GeForce 400M series. The GK107 Kepler core offers two shader blocks, called SMX, each with 192 shaders for a total of 384 shader cores that are clocked at the same speed as the processor core. Although more shader cores are available in the Kepler architecture as compared to the Fermi design, the Kepler shaders are still expected to be up to twice as power efficient. However, due to the missing hot clock of the shader domain, two shaders of a Kepler chip are as fast as one shader of a Fermi chip (the latter is clocked twice as fast). PCIe 3.0 is now supported by the mobile Kepler series and an optional Turbo mode can automatically overclock the Nvidia card by a theoretical 15 percent if the laptop cooling system allows it. The implementation of this boost mode is done in the BIOS, but it is ultimately dependent upon the manufacturer of the laptop.

Performance

The gaming performance of the GeForce GT 640M equipped with DDR3 graphics memory lies somewhere in the former 2011 high-end category between the older GeForce GT 555M and GeForce GTX 460M. The performance is exceptionally good in shader-heavy DirectX 11 games and benchmarks. However, the 128-Bit memory interface can be a bottleneck if DDR3 graphics memory is used. In our tests, demanding games of 2011 like Battlefield 3 are playable in 1366x768 and medium settings. Less demanding games, such as Modern Warfare 3, are easily playable with maxed out settings and high resolutions. Details on synthetic and gaming benchmarks performances of the GT 640M can be seen below. The more uncommon GDDR5 version of the GT 640M is slightly faster, getting closer to the DDR3 version of the GT 650M.

Features

The improved feature set now includes support for up to 4 active displays. Furthermore, high resolution monitors of up to 3840x2160 pixels can now be connected using DisplayPort 1.2 or HDMI 1.4a if available. HD-Audio codecs, such as Dolby TrueHD and DTS-HD, can be transmitted via bitstream mode through the HDMI port. However, as most laptops will feature Optimus, the integrated GPU will likely have direct control over the display ports and may limit the feature set available by the Nvidia Kepler cards.

The 5th generation PureVideo HD video processor (VP5) is also integrated in the GK107 core and offers hardware decoding of HD videos. Common codecs such as MPEG-1/2, MPEG-4 ASP, H.264 and VC1/WMV9 are fully supported up to 4K resolutions while VC1 and MPEG-4 are supported up to 1080p. Two streams can be decoded in parallel for features such as Picture-in-Picture. Another novelty is the inclusion of a dedicated video encoding engine similar to Intel QuickSync that can be accessed by the NVENCI API.

The power consumption of the GeForce GT 640M is a bit below that of the older GeForce GT 540M and more in line with the GT 525M. As a result, the Nvidia GPU is best suited for multimedia notebooks 14-inches or greater.